Methods for the treatment of regenerated cellulose thread



Patented Feb. 1, 1949 UNITED STATES PATENT METHODS FOR THE TREATMENT OF REGENERATED CELLULOSE THREAD Carl Schlatter, Wilmington, Del., and Carl V.

Holmberg, Crosseit, Aria, assignors to American Viscose Corporation, Wilmington, Del., a

corporation of Delaware No Drawing. Application July 13, 1944, Serial No. 544,824

4 Claims. (01. in-139 .5)

This invention relates to methods of treating moisture-laden filamentary material, particularly in conjunction with the manufacture of artificial filaments. 'More particularly, the invention relates to methods of treatin moisture-laden filamentary material in the form of wound packages for the purpose of drying and/or conditioning them.

The procedure of our invention is applicable to moisture-laden filamentary material of all types, but for purposes of illustration will be discussed here more particularly as used in connection with artificial filamentary material produced in accordance with the viscose process. According to that process, the spinning dope is extruded into a suitable aqueous coagulating medium, and

the thread or yarn thus obtained is collectedon 1 tion, of warm air currents circulated mainly around the packages. Unless that drying procedure is carried out very slowly, under carefully controlled temperature and humidity conditions, it results in very undesirable differences in yarn properties throughout the yarn package, which differences are most marked in the case of elongation, residual shrinkage capacities, and dyeing aifinities. Such differences are mostly due to the fact that the various portions of the yarn package are not subjected to the same drying conditions and therefore do not dry uniformly. The outer convolutions tend to dry before theinner convolution s, and because of this difference in drying rate, the outer convolutions cannot shrink during drying, so that stresses and strains are set up in the outer windings of the package, resulting in what is herein termed case-hardening" and the development of non-uniform dyeing affinities and physical properties along the entire length of the filamentary material comprising the package.

It has also been proposed to dehydrate moisture-laden'filamentary material by displacing the water by means of an organic solvent. such as 2 ethyl alcohol, hydrocarbons such as paraflin oil, solvent naphtha, etc. However, those methods of dehydration'are unsatisfactory in a number of important respects which renders them entirely unsuitable for dehydration of filamentary material particularly on a large-scale commercial basis; In the case of alcohol, for example, the

costs are excessive andit has been found that when wound packages of filamentary material are treated with alcohol, it is impossible to remove all of the adhering alcohol therefrom by centrifuging at least 15 to 20% thereof remaining in the package which is only gradually evaporated oil over a more or less extended-period of time which represents a loss of the alcohol or requires a solvent recovery system which adds considerably to the expense of manufacturing the filamentary material. The use of hydrocarbon solvents, such as solvent naphtha vor the like for dehydrating filamentary material is disadvantageous for the reason that such solvents are naturally very hydrophobic and the water-withdrawing capacity thereof is extremely low. If it is desired to effectively dehydrate moisture-laden filamentary material, and particularly wound packages of such material, by means of hydrocarbon solvents,

. such as solvent naphtha, benzene, toluene, etc.,

it is necessary to subject the material to innumerable repetitive treatments with fresh solvent over prolonged periods and at temperatures of 80 to 100 C.,which results in degradation of material, especially in the case of rayon, so that the final dried product is not suitable for the production of knitted, woven, or otherwise fabricated articles of good quality,

It is an object of the present invention to provide a method of drying filamentary material which does not involvethe disadvantages of known methods and which yields a final product of superior quality. It is a further object of the invention to provide a method of drying which greatly reduces the period of drying time. Still moisture-laden filamentary material is rapidly withdrawn therefrom in large amounts when volatile hydrocarbon solvents are applied thereto in conjunction with comparatively small amounts of an auxiliary water-withdrawing and blending agent which contains both hydrophilic and hydrophobic groups .Which are so balanced that the auxiliary agent is soluble in the hydrocarbon solvent and is capable of blending a substantial amount of water with the solvent into a single phase system having enduring stability. Such auxiliary water-withdrawing and blending agents must be sufflciently hydrophobic to be freely soluble in the hydrocarbon solvent and at the same time sufficiently hydrophilic to definitely attract water and to be appreciably soluble therein.

We have discovered that there are a number of substances which meet those requirements and which are capable of markedly enhancing the water-withdrawing capacity of volatile hydrocarbon solvents when applied in conjunction therewith. The agents contain at least one hydrophobic group, such as an aliphatic hydrocarbon group having at least 4 carbon atoms in a straight chain, in combination with hydrophilic groups, such as free hydroxyl groups, ether groups, and ester groups. The hydrophilic charactermay be the combined result of two or more such groups or it may be the result merely of one such group, but in any event, the hydrophilic content in any given compound is so balanced with respect to the hydrophobic content therein that the compound remains soluble in the volatile hydrocarbon solvent and the solution of it in such solvent can absorb a substantial amount of water without causing a separation into two or more distinct phases. An example of a highly satisfactory agent for use with solvent naphtha is the condensation product of ethylene oxide with stearic acid containing 10 ethylene oxide units per molecule. The related compounds may also be used. For example such a condensate containing 20 ethylene oxide units per molecule can be used but since it is not as soluble in the hydrocarbon as the l-unit condensate, it cannot blend as high a percentage of water and is therefore not quite as eflicient. However, such a condensate containing 40 ethylene oxide units per molecule is too hydrophilic since it is insoluble in the solvent naphthal .At the other extreme, a condensate with stearic acid containing only 5 ethylene oxide units per molecule is of reduced emciency because of reduced water-withdrawing and blending capacity. Representative hydrophobic-hydrophilic substances which may be combined with the hydrocarbon solvents are the ethers or esters of polyhydric alcohols, and especially the partial ethers and esters which contain one or more free hydroxyl groups, including such partial ethers as Butyl Cellosolve, and partial esters of such polyhydric alcohols as sorbitol, mannitol, glycol, glycerol, etc., with fatty acids such as stearic, oleic, palmitic, myristic, lauric, etc, Representative specific compounds are the distearate of a polyethylene glycol containing 20 ethylene oxide units, also Glycerol monopalmitate Glycerol monostearate Diethylene glycol mono-oleate Ethylene glycol mono-oleate Diethylene glycol mono-stearate Sorbitol distearate Sorbitol tri-stearate Sorbitol tetra-stearate or any other partial esters of the alcohols. All of the esters listed may contain ethylene oxide groups, and the number of such groups present may vary within wide limits, Such compounds as sorbitol mono-, di-, tri-, or tetra-stearate containing six ethylene oxide groups, as well as substances of the type of polyethylene glycol monostearate containing ten ethylene oxide groups have been found eflective. Esters from mixed fatty acids suchas are obtainable from fish oils, vegetable oils, or animal fats, which may or may not be hydrogenated, may likewise be used. The esters may be in their pure state or in the form of their technical grades available on the market and in that form they vary from liquid oily, or pasty or firm waxy masses which generally are readily meltable at temperatures slightly above room temperature. They are substantially neutral and do not exhibit any swelling or other untoward effect on the filamentary material.

The hydrocarbon solvents and oleaginous water-withdrawing and blending agents form clear mixtures which exist as a continuous single phase system. The mixtures do not lose their clarity or become of emulsion or suspension type even when they are passed through the yarn packages and after the water has been withdrawn from the packages and blended therewith.

According to the invention one or more auxiliary water-withdrawing and blending agents of the type aforesaid may be added to a volatile hydrocarbon solvent of the paraffinic, naphthenic or aromatic series, including such solvents of the dry cleaning type derived from natural sources as Stoddards solvent, th naphthenes or cycloparaflins, aromatic hydrocarbons such as benzene, toluene, solvent naphtha, the xylenes, or similar solvents. The hydrocarbons are solvents for the auxiliary water-withdrawing and blending agents, are normally immiscible with water but capable of being blended therewith in the presence of the auxiliary agent and do not adversely affect the filamentary material. To form the dehydration medium, the auxiliary blending agent may be added to the hydrocarbon solvent in any suitable amount, comparatively small quantities in the neighborhood of about 1 to 10% by weight being satisfactory, and depending upon the particular blending agent or agents selected, some improvement in efliciency may be noticeable at the higher concentrations. The temperature at which dehydration is eifected may vary from about room temperature to around 100' C., temperatures in the neighborhood of about C. having been found to be good practical working temperatures in most cases. The temperature should not be as high as or above the boiling pointof water or the dehydration medium under the conditions of application.

The dehydration process may be carried out in any suitable manner. In the case of rayon cakes or other wound packages, it is advantageous to support the packages on a perforated pipe or tube and to pump the dehydrating solution or dispersion therethrough so that the same is forced through the package from the inside to the outside thereof. In this manner, dehydration of the packages proceeds uniformly, essentially from the inside of the packages, so that opportunity for the development of internalstrains in the package does not occur and all of the layers constituting the various strata of the package are dried at substantially the same rapid rate and under practically the same temperature conditions. The amount of water withdrawn may be controlled, and dehydration may be so elected that the packages or cakes retain substantially the moisture content normally desired i'n commercial grades of filamentary material which, in

the case of regenerated cellulose, for example. is about 11%, or the method may be applied in connection with procedures in which the removal of the moisture is effected in separate stages of a multiple stage process. In some instances, it may be preferred to partially dehydrate the package by as a combination simultaneous dehydrating and conditioning operation in which the. conditioning agent isapplied to the filamentary material while: the latter is in the moist condition. The

amount of conditioning or lubricating agent, i. =e.

of an auxiliary water-withdrawing and blending agent of oleaginous character or of waxy char acter where it is desired to size or set the twist 'of yarns or fabrics remaining on the filamentary means of comparatively small amounts of the hyfor hydrocarbon solvents) is left to evaporate and as such solvents are inexpensive thisls no economic handicap; Also such evaporation causes no case hardening and all parts of the 'cake are uniformlydried and of uniform quality.

The application of a dehydrating solution in,

accordance with the instant invention to moisture-laden wound packages of filamentary material results in a striking improvement in the rate and amount of water withdrawn therefrom, and a consequent marked reduction in drying time, the solution having the capacity of withdrawing water inthe amount of 10,000 to 100,000 or more parts of water to a million parts thereof, as contrasted to two parts of water withdrawn by a million parts of hydrocarbon solvent when the latter only is applied to the filamentary material under comparable temperature conditions. It has been determined by repeated experiment that, whereas drying methods involving the circulation of warm air currents require at least three days, and the use of hydrocarbon solvents alone requires about the same time or longer, in the present case the packages are satisfactorily dried in a matter of about three hours or less depending on the speed of circulation of the medium.

The dehydrating medium may be applied to moisture-laden filamentary material in a form other than a wound package as for example to fibers in the form of a tow, felt or fabric, or to running lengths thereof, the fibers or articles comprising the same being continuously drawn through a path along which they come into con.-

material after withdrawal of the water there.- from may be predetermined and variedwithin fairly wide limits by controlling the temperature at which the dehydrating process is carried out, the particular oleaginous or waxy waterwithdrawing and blending agent selected, and the concentration thereof employed, so that a wide latitude in these conditions is possible and permissible for obtaining special results. Although the oleaginous or waxy water-withdrawing and blending agent is hydrophobic to some'extentit is sufllciently hydrophilic to permit of its being removed from fabrics made from the treated filamentary material by ordinary scouring methods. As examplesof our invention, when a dehydrating medium consisting of Stoddards solvent and 5% by weight of sorbitol distearate containing six ethylene oxide groups was passed from the inside through all parts of moist rayon cakes at 80C., about 8 to 10% of the sorbitol distearate compound remained on the material after withdrawal of the water therefrom. 0n the other hand, after. the water was withdrawn from moist cakes by-' vantages when applied to rayon cakes or other wound packages since it facilitates even and thorough penetration of the conditioning agent tact with the medium which may be sprayed on or otherwise applied thereto.

Preferably, after the dehydrating medium has been passed through the wound package or applied to fibers in other forms, it is recycled and water evaporated therefrom in order to'mainyarn or the like. Since the preferred blending agents are of the lubricating type of substance which is frequently applied to filamentary material preparatory to textile processing thereof, for

example, to render the same more easily manipulable in knitting and weaving operations, that is to facilitate passage of the filaments through the knitting or weaving machines, the presence throughout all strata of thepackage, the agent taking the place of withdrawn water, and there is no tendencyforthe conditioning agent tomigrate from one stratum of the package to another upon the final removal of excess dehydrating medium, such as is oftenexperienced when lubricating or other conditioning agents 7 are'applied to wound packages of filamentary material from simple solutions thereof in aqueous or organic solvents. This appears to be the result of a definite partitioning ratio between the filamentary material and the blended dehydrating medium-watersolution;

A striking feature of the present invention resides in the fact that the dried product obtained by means of our new dehydrating procedure is of decidedly diflerentand vastly superior quality of the blending agent on the material is not ob- .iectionable and may be highly desirable and in'-- tentional. Thus, our invention may be regarded other methods, being characterized by greater softness and pl-iability and an improved fiufly handle or feel, which is obtained without any 1m: pairment in elongation, tensile strength, or other desirable physical property. This marked superiority of the dried material as to softness and increased workability apparently results from the use of the auxiliary water-withdrawing and blending agent in the dehydration procedure, but is not due merely to the presence thereof on the dried material, since the improvement is observedregardless of the amount thereof remaining on the material, and-even when only minute amounts are present. A dried product of 7 the same or comparable quality cannot be obtained by any other known drying method, and is not obtained when filamentary material which has been previously dried by such known methods is subsequently impregnated with a lubricant or conditioning agent in a separate operation.

To illustrate one method of practicing our invention, cakes comprising freshly spun viscose rayon coming directly from the last washing stage of the after-treatment stages of the viscose rayon process, including bleaching, desulfurizing, and washing were centrifuged to remove excess surface water, after which they contained about 150 to 200% of water. A solution consisting of Stoddards solvent and of sorbitol distearate containing six ethylene oxide groups, at 80 0., was then passed through the cakes from the inside to the outside thereof. After three hours, the cakes were centrifuged and the water content was found to have been reduced to about 10% on a bone-dry basis, and about 10% of the sorbitol distearate compound remained on the filamentary material.

Instead of the dehydrating medium employed above, a solution consisting of any other similar partial ester of a polyhydric alcohol, or partial ether thereof, and any other hydrocarbon or chlorinated hydrocarbon solvent may be employed.

While the invention is particularly suitable for the initial dehydration of freshly produced regenerated cellulose rayon in wound package form, it is not limited thereto, and may be applied with similar noteworthy results to other textile materials such as yarns of cotton, wool, real silk, cellulose acetate, or other natural or artificial fibers.

From the foregoing discussion,it will be apparent that we have devised an entirely new method of rapidly dehydrating and conditioning moisture-laden filamentary material by means of which it is possible to utilize the readily available and cheap hydrocarbon or chlorinated hydrocarbon dry-cleaning solvents modified by the incorporation therewith of only relatively small amounts of auxiliary water-withdrawing and blending agents. The process is simple, extremely economical, and yields a dried product which is of high quality, characterized by uniform tensile strengths, residual shrinkage capacities, and dyeing aflinities throughout and which is suitable for working into knitted, woven or otherwise constructed fabrics of uniformly good quality. The fact that the process may be so practiced as to result in the simultaneous dehydration and conditioning of the filamentary material to any desired extent is of special consideration in some cases, since it eliminates the necessity for subjecting the material to separate lubricating, sizing, twist-setting, or other conditioning procedures in those instances where the presence of the conditioning agents in appreciable amounts is desired or necessary.

While preferred embodiments of the invention have been described, the description herein is intended to be illustrative only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the invention as defined by the appended claims.

We claim:

1. In the method of manufacturing artificial filaments of regenerated cellulose from viscose comprising spinning the filament-forming material into an aqueous coagulating medium and subjecting the filaments to aqueous after-treatment, including final washing, the step of continuously over a predetermined interval of time treating the filaments while still wet from the washing step and before any prior drying thereof, with a solution comprising a volatile hydrophobic hydrocarbon solvent and from about 1 to 10% of an organic compound capable of withdrawing water from the filamentary material and blending the withdrawn water with the hydrocarbon solvent into a substantially single phase system, said organic compound being soluble in the hydrocarbon solvent, containing at least one hydrophobic group and at least one hydrophilic group, and comprising a substance selected from the group consisting of partial esters of polyhydrlc alcohols with fatty acids having from 12 to 18 carbon atoms, and ethylene oxide condensates of such esters containing from 6 to 20 ethylene oxide units, such treatment being performed at a temperature below the boiling points of water and the solvent under the conditions of application, and continuously removing the resulting blended system from the filamentary material thereby leaving the material in a predetermined state of dryness.

2. Ina method of manufacturing regenerated cellulose thread from viscose, the step of treating a moisture-laden wound package of the thread, after washing thereof as a stage in its manufacture and before any prior drying thereof, which comprises continuously passing through all parts of the package a solution comprising a hydrocarbon dry-cleaning solvent and from about 1 to 10% by weight of a sorbitol partial stearate containing six ethylene oxide groups, and continuously removing water carried by the thread in a blended, single phase system with the hydrocarbon dry cleaning solvent and polyhydric alcohol derivative.

3. In a method of manufacturing regenerated cellulose thread from viscose, the step of treating a moisture-laden wound package of the thread, after washing thereof as a stage in its manufacture and before any prior drying thereof, which comprises continuously passing through all parts of the package a solution comprising Stoddards solvent and 5% by weight of sorbitol distearate containing six ethylene oxide groups, said treatment being performed at a temperature of about C., and continuously removing water carried by the thread in a blended, single phase system with the hydrocarbon dry cleaning solvent and polyhydric alcohol derivative.

4. In a method of manufacturing regenerated cellulose thread from viscose, the step of treating a moisture-laden wound package of the thread, after washing thereof as a stage in its manufacture and before any prior drying thereof, which comprises continuously passing through all parts of the package a solution comprising Stoddards solvent and 5% by weight of polyethylene glycol distearate containing twenty ethylene oxide groups, said treatment being performed at a temperature of about 70 C., and continuously removing water carried by the thread in a blended, single phase system with the hydrocarbon dry cleaning solvent and polyhydric alcohol derivative.

CARL SCHLAT'I'ER. CARL V. HOLMBERG.

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